Any surround better than none at all?

In your case I would try to get a center speaker that is a good match for your mains and not worry as much about the rears for now. In the mean time I would just use what you have for movies, if your room will allow for it you might be able to set it up with no center at all (works best in larger rooms). I have never watched a newer movie that was in DD or DTS that sounded better without surround and can only laugh to my self when I hear someone try to tell people other wize. Enjoy your movies.

I think almost any surround is better than nothing. I am definitely a dedicated two channel guy, but I would prefer Radio Shack for sides (rear) than nothing at all.

Movies are for fun. One of the few times the entire family sits together to listen. My mother in law will even venture over if she knows we rented DVD's for the weekend.

As already stated, enjoy your movies. It might even help gain more acceptance for your two channel.

Your comment requesting us Audiogon users to "be gentle" is not so far from the mark I suppose! The audiophile breed is amoung the most critical on the planet it appears! (no toys to play with when we were kids...)
Anyway, my suggestions would be to not use any center or rears at all if you can't use the same speakers as you have now for those purposes! If you use mismatched speakers, no matter how close, it will only bring the integrity, believability, and coherence of the system DOWN! You'd be best served by simply using your main left and rights with a sub through your pre/pro!(which you MUST use for proper movie playback of DD/DTS).
Another solution is to buy a whole nother set of even less expensive, but more movie friendly/effective HT speakers/satalites. This way you don't sacrifice the integrity of either your HT or music. You could mount 5 or more matching HT speakers around the room(maybe a dedicated matching center over or under the TV/monitor/screen), and potentially have a much more effective HT system. There are compromises here however in terms of set up for best sound, and an EQ might be in the works. Still, the integrity of movie soundtracks isn't what a good 2 channel recording is ultimately. However, If you're happy with what you get from your 2 channel system for movies, you might just consider keeping those two set up "as-is", and integrating the subwoofer. There are of course lots of options. But if you plan on keeping the 2 you have, and doing 5.1 or better, you will need matching speakers, not similar sounding speakers! If you don't want another speakers system for movies, and 2 channel is your priority, you might just keep things as they are. I pressently have a 2 channel set up with sub and processor for my movies, and it sounds great.(but then it's set up well.)
My thinking is that I'd take a quality 2 channel set up(integrated with proper digital pre/pro and such) over not so well executed multi channel every time! So it must balance.
good luck

I'd suggest using a "phantom center" setting on your processor rather than using a mis-matched and sub-standard center, since the center channel carries so much of the load in most soundtracks. But I agree with Albert Porter...any surrounds will enhance your enjoyment of movies. Make sure you set the levels accurately...you don't want the surrounds to be a distraction.

I totally agree with Rsuminsby, use a "phantom" center and any ol' surround speakers.